1. Field of the Invention
The present invention relates to an improved infrared ray detector that can be used, for example, on an air-to-fuel ratio meter and the like and, more particularly, to an infrared ray detector assembly having an improved construction to remove noise while monitoring a plurality of wavelengths.
2. Description of the Prior Art
The prior art is aware of the need to monitor a plurality of components from a single source such as the exhaust of an automobile.
A selective infrared ray detector comprising a plurality of infrared ray detecting elements and a plurality of optical filters arranged corresponding to each respective infrared ray detecting elements has been disclosed in, for example, Japanese Patent Application Laid-Open No. Sho 50-17276. This detector is provided with three separate chambers, each having a concave section formed independently in a housing body. An infrared ray detecting element is arranged in each of the respective three chambers and optical filters for transmitting predetermined wavelength bands of infrared rays, corresponding to components to be measured, are inserted into entrance portions of the respective chambers and mounted on the housing of the infrared ray detector. In this infrared ray detector, the infrared rays, which have been transmitted through the respective optical filters, are incident upon the respective infrared ray detecting elements to provide output signals.
Spectral characteristics of the optical filters can be shifted to longer wavelengths with a temperature rise, and each of the respective optical filters can further have a different transmission wavelength band shifting. An infrared ray detector adapted to enable the regulation of the temperature of optical filters, in order to prevent such influences from affecting the performance of the optical filters, has been disclosed in Japanese Utility Model Publication No. Sho 60-4110. In this infrared ray detector, optical filters are arranged at respective end portions, which are separated from each other and stand side by side, of optical inlet ports to provide a V letter-shape in a metallic block while optical sensors are mounted on substrates arranged at the other end portions of the optical inlet ports. The metallic block is provided with a temperature sensor, and an endothermic-exothermic element is mounted on a side portion thereof at a distance from the optical filter and the optical sensor. The temperature of the metallic block is detected by the temperature sensor. The metallic block is subsequently cooled or heated by the endothermic-exothermic element on the basis of an output signal from the temperature sensor to regulate the temperature of the metallic block, thereby holding the optical sensor and the optical filter at a constant temperature.
An infrared ray detector provided with an infrared ray detecting element arranged in a cylindrical case has also been disclosed in Japanese Utility Model Application Laid-Open No. Sho 64-48637. In this infrared ray detector, a substrate is arranged in a cylindrical case formed of metal having an opening which is closed with a window material transmissible to an appointed wavelength band of infrared rays. A substrate is provided with an infrared ray detecting element mounted thereon. The infrared rays, which have been transmitted through the window material, are incident upon the infrared ray detecting element to provide an output signal.
An infrared ray detector disclosed in Japanese Patent Application Laid-Open No. Sho 50-17276 detects three separate components, but a disadvantage occurs in that its sensitivity is relatively low. In other words, the quantity of measuring signal is small.
An infrared ray detector disclosed in Japanese Utility Model Publication No. Sho 60-4110 is adapted to prevent any temperature change of the optical sensor and optical filter. The temperature change of the metallic block is detected and the temperature is regulated to hold the optical sensor and optical filter at a constant temperature. However, since there are differences in distance from the respective optical filters to the endothermic-exothermic element in view of the positional relationship between the endothermic-exothermic element provided on the metallic block and the two optical filters, it is difficult to regulate the temperature of both optical filters under the same condition. Thus, the temperature change of an optical filter distant from the endothermic-exothermic element is increased. In addition, since the optical sensor is mounted on the metallic sensor through the substrate, a time lag is also produced in the regulation of the optical sensor temperature.
In the infrared ray detector disclosed in Japanese Utility Model Application Laid-Open No. Sho 64-48637, the infrared ray detecting element is arranged to provide a window in an opening portion, but a side wall of the case is positioned around this infrared ray detecting element. Accordingly, the infrared rays, which have been transmitted through the window material are incident upon the inside of the case, and stray light, which has been incident upon an inner surface and the like of the case and reflected from there, are directly incident upon the infrared ray detecting element. Thus a problem can occur in that interference is apt to be produced with resulting noise in the output signals.
In the infrared ray detector disclosed in Japanese Patent Application Laid-Open No. Sho 50-17276, the entire optical filter is inserted into the entrance portion of three chambers, which are independently formed in the body of the infrared ray detector, respectively. Accordingly, a problem has occurred in that the cost of installing the respective optical filters is increased.
In addition, if the respective optical filters are placed in the entrance portion of the respective chambers, the optical filters can be easily installed. However, a problem can still occur in that light can leak from an end face of the optical filter, if it is not properly sealed, to produce interference.
Furthermore, if the respective substrates composing the respective optical filters are different in material, the processing procedures for the respective substrates are different depending upon the substrate conditions, such as the hardness of the respective material, so that the respective substrates can have a difference in thickness in many cases. Accordingly, if a plurality of substrates 21, 21' having different thicknesses are positioned side by side because of the difference in material, as shown in, for example, FIG. 7, step 22 is produced at the end faces of the substrates 21, 21'. If the infrared rays are incident upon the substrates 21, 21', a problem can occur in that light can leak from the step 22 to interfere with each filter.